The present invention relates to vascular prosthetic devices such as grafts and stents, especially of the elastic type that can be compressed to a reduced radius for delivery. The invention further concerns systems for delivering the prostheses to their intended intralumenal treatment sites, and means for securing the prostheses at their respective sites.
The vascular graft is a useful device for treating aneurysms and other blood vessel abnormalities. Common aneurysms result from weak blood vessel walls that typically balloon outward from the intrinsic pressure in the vessel. Aneurysms can apply pressure on adjacent anatomic structures producing abnormal functions. Also, the affected vessels have a potential to split and rupture, thus causing internal bleeding and potentially life-threatening conditions. In addition to common aneurysms, dissecting aneurysms involve a fissure in the internal wall of the vessel. Blood flows through the fissure and can collect between the internal wall and the outer wall, causing the vessel wall to swell.
A vascular graft can isolate an aneurysm or other blood vessel abnormality from the blood pool, reducing pressure on the weak vessel wall. The graft also can reduce blood loss, should the vessel rupture. Ideally, the graft provides reinforcement at the weakened part of the vessel, reduces pressure on the vessel wall, and minimizes blood flow into the space between the graft and the aneurysm while allowing blood flow through an internal lumen of the graft without the formation of thrombus. The graft should remain secured in place, despite the pulsations of the vessel due to the pumping action of the heart.
To isolate aneurysms, physicians have surgically removed them and sutured graft material in place. Attempts to percutaneously insert and place grafts into target vessels have involved grafts made of an inelastic textile, fixed through the use of hooks or expandable stents. Delivering and deploying such grafts typically involves a catheter or other device to carry the graft to the target vessel and to the treatment site within the target vessel. Then, a balloon is inflated to expand the graft and attachment structures. Usually the physician must inflate and deflate the balloon repeatedly to expand the graft without continuously occluding the vessel. The inflation/deflation cycles can weaken the balloon. Such grafts frequently experience leaks between the graft and the blood vessel wall. The attachment structures are susceptible to fatigue failure. Frequently, there is less than the desired degree of contiguous contact of a graft material with the blood vessel interior wall. Such contact is desirable, because the graft textiles are potentially thrombogenic due to their rough weave, and contact thus promotes healing of the aneurysm by forming a thin cellular layer between the vessel and the graft.
The required delivery systems are cumbersome in their manufacture and use. More particularly, the need for balloons requires assurance that each balloon has an adequate burst strength to withstand pressures required to enlarge the graft and attach the graft support structures to the vessel wall. Single chamber balloons occlude the vessel wall when they are expanded. Moreover, balloon inflation has the potential to overexpand the vessel wall, which can cause endothelial cracking, promote restenosis or even rupture the vessel. Also, whenever the balloon is deflated before the graft is secured to the vessel wall, there is a risk that blood flow will shift the graft axially away from its intended location. Finally, conventional grafts must be provided in many different sizes, since each graft is limited as to the range of blood vessel diameters that it can accommodate.
Another type of intravascular prosthesis is the radially expandable stent, frequently used to counteract restenosis of a vessel following a translumenal angioplasty procedure. Typically, balloons are used to open the vessel wall and to expand the stent. Size and burst pressure considerations limit the efficacy of balloons in expanding the stent. Often, multiple balloons are required to expand a single stent, due to the tendency of balloons to burst during stent expansion.
A frequently encountered problem is an aneurysm or other abnormality in a branched vessel. Prosthesis with corresponding junctions, frequently called "Y" grafts, have been used to isolate such abnormalities from the blood flow. Such grafts, which typically involve several tubular structures, are difficult to deploy and secure at the intended treatment site, requiring either maneuvering of a preassembled graft in opposite axial directions, insertion of a tubular structure into another after their approximate placement, or both.
Therefore, it is an object of the present invention to provide an implantable prosthesis formable into a reduced-radius profile to facilitate its delivery to a site of intralumenal implantation, then radially enlargeable at the site without balloons or other devices.
Another object is to provide a more effective fixation of an implantable prosthesis within a body lumen, and in connection with grafts a more effective seal against leakage.
A further object is to provide an improved system for deploying prostheses, preferably enabling retraction of a partially deployed prosthesis for repositioning along a lumen if desired.
Yet another object is to provide an implantable prosthesis that is easier to deploy within branched vessels and more effectively fluid-isolates aneurysms and other abnormalities occurring in branched vessels.